1. Technical Field
The disclosure relates to a rotary electric machine and in particular, to a rotary electric machine which is provided with an embedded magnet type rotor.
2. Description of Related Art
With respect to a rotary electric machine which is used in an electric vehicle, in order to attain reduction in size and weight and improvement in output efficiency, an embedded magnet type rotary electric machine is used in which a plurality of permanent magnets is embedded along a circumferential direction in a rotor core to form magnetic poles. The embedded magnet type rotary electric machine outputs combined torque of magnetic torque which is generated by cooperation of a rotating magnetic field of a stator with the permanent magnets and reluctance torque which is generated based on a magnetic anisotropy of the rotor core. By disposing a plurality of embedded magnets in a V-shape within one magnetic pole, it is possible to further improve the output efficiency, and by disposing the embedded magnets in two layers along a radial direction, it is possible to further increase torque that can be output.
In Japanese Unexamined Patent Application Publication No. 2011-223836 (JP 2011-223836 A), with respect to a two-layered embedded magnet type rotary electric machine, a magnetic field analysis using an optimal distance index γ=β/α, in which a magnet-to-magnet distance along a radial direction between a V-shaped permanent magnet which is disposed on the inside and a V-shaped permanent magnet which is disposed on the outside is set to be β and the radius of a rotor is set to be α, is described.
In a two-layered embedded magnet type rotary electric machine of Japanese Unexamined Patent Application Publication No. 2007-274798 (JP 2007-274798 A), a permanent magnet which is disposed on the outer peripheral side is susceptible to demagnetization during field weakening, and therefore, permanent magnets having two types of shapes; a permanent magnet which is disposed on the inner peripheral side, and a permanent magnet which is disposed on the outer peripheral side and has a narrower width and a greater thickness than the permanent magnet which is disposed on the inner peripheral side, are used to be divided.
In Japanese Unexamined Patent Application Publication No. 2005-198487 (JP 2005-198487 A), it is mentioned that in a multilayered embedded magnet type rotary electric machine, stress acting on a center bridge between permanent magnets adjacent to each other due to a centrifugal force or an excitation force due to the rotation of the rotary electric machine increases as the mass of an embedded magnet becomes larger. It is disclosed that the permanent magnet becomes longer in length along a circumferential direction and larger in mass as it moves toward a layer which is disposed on the inner peripheral side along a radial direction in a multilayer, and therefore, the length along the circumferential direction of the center bridge is increased accordingly.